The invention relates to a control system and method for preventing exhaust gases from entering an intake manifold of an engine after engine shutdown.
Engines have long used throttle valves and idle air control valves to adjust the amount of airflow into engine intake manifolds. Generally, a powertrain controller generates first and second control signals to control operational positions of the throttle valve and the idle air control valve, respectively.
When an engine is shutdown, the throttle valve and idle air control valve are generally closed. As a result, the air pressure in the intake manifold has a relatively low pressure (i.e., a vacuum) compared to the pressure of exhaust gases in an exhaust manifold. Further, after engine shutdown, intake and exhaust valves communicating with an engine cylinder may overlap in an open position. As a result, the exhaust gas in the exhaust manifold may migrate through the engine cylinder and into the intake manifold. Thereafter, during engine crank, the exhaust gases in the intake manifold must be pumped through the engine cylinders before sufficient oxygen is supplied to the cylinders for combustion to occur. Thus, the migration of exhaust gases into the intake manifold, after engine shutdown, results in a long engine crank (i.e., startup time) that is undesirable to vehicle operators.
The above-identified disadvantages of conventional control systems and methods are substantially overcome by a control system and method described and claimed herein.
A method for preventing exhaust gases from entering the intake manifold after engine shutdown in accordance with the present invention is provided. The engine includes a valve controlling airflow into the intake manifold. The method includes determining when the engine has been shutdown. The method further includes opening a valve for a predetermined amount of time after engine shutdown to allow air at an ambient atmospheric pressure to communicate with the intake manifold.
A control system for preventing exhaust gases from entering an intake manifold after engine shutdown in accordance with the present invention is provided. The control system includes a valve actuator configured to control an operational position of a valve controlling air flow into the intake manifold, responsive to a control signal. The control system further includes a control circuit that is operably connected to the valve actuator. The control circuit is configured to determine when the engine has been shutdown. The control circuit is further configured to generate a control signal to induce the valve actuator to open the valve for a predetermined amount of time after engine shutdown to allow air at ambient atmospheric pressure to communicate with the intake manifold.
The control system and method for preventing exhaust gas from entering an intake manifold of an engine after engine shutdown provides a substantial advantage over conventional systems and methods. In particular, the control system increases the air pressure in the intake manifold to ambient atmospheric pressure after engine shutdown. As a result, exhaust gases remain substantially within the exhaust manifold after engine shutdown. Thereafter, the engine may be started quickly because fresh air is immediately inducted into the engine cylinders during engine crank.